FIG. 1 shows an electro-drive type fuel pump of an in-tank system, which is installed in a fuel tank. The electro-drive type fuel pump illustrated in FIG. 1 is composed of a motor portion 1 and a pump portion 2, which are incorporated in a cylindrically formed housing 3. A motor cover 4 and a pump cover 5 are attached to the upper and lower end portions of the ahousing 3.
By supporting the upper and lower end portions of a shaft 8 at the motor cover 4 and the pump cover 5 via bearings 9 and 10, respectively, an armature 7 is disposed in a motor chamber 6 so as to rotate therein. A plurality of commutator segments 12, which are connected to a coil and which are composed of copper and silver as their principal components, are disposed on the armature 7 and are insulated from each other. A magnet 11 is disposed on the inner wall surface of the housing 3. A brush 13, which can slidingly contact the commutator segments 12 of the armature 7, and a spring 14 that biases the brush 13 are incorporated in the motor cover 4. The brush 13 is connected to an external connection terminal via a choke coil 15.
A check valve 17 is incorporated in a discharge port 16 secured to the motor cover 4, and a fuel feeding pipe is connected to the discharge port 16. A pump body 18 is attached to the lower end portion of the housing 3 by caulking it to the lower side of the pump cover 5. A fuel inlet opening 19 is provided in the pump body 18 and a fuel outlet opening 20 is provided in the pump cover 5. The inlet opening 19 and the outlet opening 20 are provided at positions separated from each other in the circumferential direction of the pump chamber formed by the pump body 18 and pump cover 5. A disk-shaped impeller 21 having a plurality of blade grooves 22 formed on the upper and lower sides in the circumferential direction is disposed in the pump chamber formed by the pump body 18 and the pump cover 5. The impeller 21 is formed of resin, etc., and is fitted onto the shaft 8 of the armature 7.
In an electro-drive type fuel pump constructed as described above, when the motor portion 1 is energized to rotate the armature shaft 8, the impeller 21 is driven for rotation. As the result, fuel in the fuel tank is drawn up through the inlet opening 19 and enters the motor chamber 6 through the outlet opening 20, and the fuel is discharged to a fuel feeding pipe through the discharge portion 16.
A known impeller is described in Japanese Laid-open Patent Publication No. 7-54726. FIGS. 2 through 5 show the known impeller. FIG. 2 is a perspective view of the impeller, FIG. 3 is an enlarged view of section III identified in FIG. 2, FIG. 4 is a sectional view (sectional view taken in the radial direction) taken along the line IV--IV in FIG. 3 and FIG. 5 is a sectional view (sectional view taken in the circumferential direction) taken along the line V--V in FIG. 3. Blades 23 are provided along the circumferential direction on the outer circumferential portion of both sides of the impeller 21 and a blade groove 22 is formed between the blades 23. A flow line groove 35 is formed at portions of the pump cover 5 and the pump body 18 that correspond to the blade grooves 22 of the impeller 21. Thus, the flow line groove 35 forms a flow line 36 from the inlet opening 19 to the outlet opening 20. In the radial direction sectional view, the blade grooves 22 are formed in a curved shape as shown in FIG. 4.
Furthermore, in the circumferential direction view, the blade grooves 22 are formed in a rectilinear shape that is parallel to the plane of the impeller as shown in FIG. 5. The connection portion 26 between the end face 24 of the blade 23 at the front side of the rotational direction and the end face 25 of the blade 23 at the rear side of the rotational direction has a right angle, that is, a rectangular shape. An opening portion of the blade groove 22 is formed so that the opening edge portion 28 in the radial direction at the rear side of the rotational direction has a rectilinear shape as shown in FIG. 3, and at the same time, connection portions 31 and 32 between the opening edge portion 28 and the opening edge portion 29 or 30 in the circumferential direction has a right angle.
In such a known impeller 21, when fuel flows from the inlet opening 19 to the outlet opening 20, a circulating vortex flow is generated wherein fuel flows outward of the radial direction along the blade grooves 22 of the impeller 21 as shown by the arrows in FIG. 4 and collides with the wall surface in the radial direction of the flow line 36. The fuel flows inwardly in the radial direction along the flow line groove 35 and again flows outward of the radial direction along the blade grooves 22. Because the speed of the circulating vortex flow in the circumferential direction is slower than the peripheral speed of the impeller 21, the fuel that flows inwardly in the radial direction along the flow line groove 36 is caused to flow in the blade grooves 22 at the rear side of the rotational direction. At this time, because the connection portions between the blade grooves 22 and the end faces 24 or 25 of the blade 23 are formed to a right angle when viewed in the circumferential direction, the speed of the circulating vortex flow in the circumferential direction is decelerated by fluid resistance at the right angled connection portion 26, and thus, pump efficiency was not satisfactory.
Furthermore, an impeller in which blades are inclined in the rotational direction as described in Japanese Laid-open Patent Publication No. 6-299983, and an impeller in which the blades are chamfered as described in Japanese Laid-open Patent Publication No. 7-189973, etc., has been described.
However, with respect to impellers in which blades are inclined in the rotational direction and blades or chamfered, the number of resin materials can form the impeller are limited, because the impeller shape is complicated. In particular, it becomes difficult to mold the impellers with thermosetting resin. Because the strength, anti-swelling properties when contacting with gasoline, etc., of thermosetting resins are higher than those of thermoplastic resins, etc., reliability may be a problem if the impellers are made of a resin such as thermoplastic resin, etc., other than the thermosetting resin, etc.
Further, because the opening edge portion 28 in the radial direction at the rear side of the rotational direction of the opening portion of the blade grooves 22 shown in FIG. 3 has a rectilinear shape, and the connection portions 31 and 32 between the opening edge portion 28 and the opening edge portion 29 in the circumferential direction outward of the radial direction or the opening edge portion 30 in the circumferential direction inwardly in the eradial direction have a right angle, the speed of a circulating vortex flow flowing out from the blade grooves 22 in the circumferential direction is decelerated, and inflow of fuel into the blade grooves 22 is not smooth. Therefore, pump efficiency is not satisfactory.
In addition, although vapor exhaust port 37 that exhausts vapor (air bubbles) in the blade grooves 22 is disposed in one flow line groove 35 of the pump cover 5 or the pump body 18, vapor in the blade grooves 22 that is disposed in the side opposite of the vapor exhaust port 37 cannot be immediately exhausted through the vapor exhaust port 37. Therefore, pump efficiency is not satisfactory. Further, because the outlet opening 20 is provided at one side (the upper side in the case of FIG. 1) of both upper and lower sides of the impeller 21, fuel in the blade grooves 22 opposite to the side where the outlet opening 20 is disposed scarcely flows into the outlet opening 20 side. Therefore, pump efficiency is not satisfactory.
It is, accordingly, an object of the invention to provide an impeller for an electro-drive type fuel pump that is capable of improving pump efficiency with a simple shape or construction.